Last checked at 
* UK reports five cases of blood clots due to vaccines
* 11 million people have had AstraZeneca's vaccine in UK
* PM Johnson lauds vaccine safety, says getting shot
* Benefits of the shot far outweigh possible risks, MHRA
says
(Adds PM, chief medical officer, Oxford)
By Alistair Smout
LONDON, March 18 (Reuters) - Britain's medicines regulator
on Thursday gave its continued backing to AstraZeneca's COVID-19
vaccine, saying the benefits outweighed the risks after finding
there had been five cases of a rare brain blood clot among 11
million administered shots.
Britain's Medicines and Healthcare products Regulatory
Agency (MHRA) said that use of the vaccine should continue while
the five reports were investigated, and one official said that
the rollout would likely continue even if a link was proved.
Concerns about reports of blood clots, along with low
platelet levels, have led to some European countries including
Germany to pause the rollout of the shot while the cases were
investigated by the European Medicines Agency (EMA).
The EMA announced later on Thursday that the vaccine was
"safe and effective", and also said the benefits outweighed
risks, even if a link between blood clots in the brain and the
shot could not be definitively ruled out.
"The Oxford jab is safe and the Pfizer jab is safe. The
thing that isn't safe is catching COVID which is why it's so
important that we all get our jabs as soon as our turn comes,"
British Prime Minister Boris Johnson said at a news conference
in Downing Street.
"As it happens I'm getting mine tomorrow, and the centre
where I'm getting jabbed is currently using the
Oxford/AstraZeneca vaccine ... and that is the one I'll be
having."
June Raine, Chief Executive of the UK's MHRA, said there was
"no evidence that blood clots in veins is occurring more than
would be expected in the absence of vaccination, for either
vaccine," referring to AstraZeneca and Pfizer shots.
Raine said there had been a very small number of reports of
an extremely rare form of blood clot in the cerebral veins
(sinus vein thrombosis, or CSVT) occurring together with lowered
platelets soon after vaccination, and a review of the cases was
ongoing.
"Given the extremely rare rate of occurrence of these CSVT
events among the 11 million people vaccinated (with
AstraZeneca), and as a link to the vaccine is unproven, the
benefits of the vaccine in preventing COVID-19, with its
associated risk of hospitalisation and death, continue to
outweigh the risks of potential side effects," she said.
The University of Oxford, which developed the vaccine,
welcomed the determination of the MHRA and the EMA, adding that
the rollout of the vaccines should continue to be monitored.
CVST is a rare form of stroke caused by a blood clot that
prevents blood from draining out of the brain.
One of the five reported cases was fatal, MHRA Vaccine
Safety Lead Philip Bryan said, adding that the cases were all
among men aged between 19 and 59.
Asked if any cases had also been reported from the rollout
of the Pfizer vaccine, Bryan said that while there had been two
cases of sinus thrombosis, they had not been accompanied with
the thrombocytopenia - low platelet levels - that had been
specific characteristics of the reports among those given
AstraZeneca shots.
"The specific cases we're looking at is that combination of
events (of CVST and thrombocytopenia)" he said.
NO PAUSE NECESSARY
The MHRA said anyone with a headache that lasts for more
than four days after vaccination, or bruising beyond the site of
vaccination after a few days, should seek medical attention.
But Munir Pirmohamed, Chair of the Commission on Human
Medicines, in a statement suggested that even if a link between
the clots and the vaccine was established, it likely wouldn't
halt Britain's rollout.
"If we feel that there's causal link then we may need to
update the product information, but overall, I don't think that
would necessitate pause to any kind of vaccination programme,"
he told reporters in a briefing.
Stephen Evans, at the London School of Hygiene and Tropical
Medicine, said that COVID-19 itself was associated with similar
symptoms, making causality hard to establish.
"A major problem is discerning whether there is a
possibility that this was caused by COVID-19," Evans told
Reuters.
"Exactly these sort of conditions have been seen in patients
with COVID-19 prior to the vaccines being available."
(Reporting by Alistair Smout and Guy Faulconbridge, additional
reporting by Kate Holton, Estelle Shirbon, Paul Sandle and Kate
Kelland; Editing by Nick Macfie and Elaine Hardcastle)
